The long rail is actually an antenna.
It is used for the EAS system. EAS is the french short for Equipement à Agent Seul, which means "sole-agent equipment". The antenna is used to transmit the video feeds of the platorm's cameras to screens inside the driving cab.
The driver is able to remotely close or open the doors while watching for any incident, ...
There are three stations:
Heathrow Terminals 2&3
Heathrow Terminal 4
Heathrow Terminal 5
(Note that 2, 3, 4 and 5 are the only terminals: Terminal 1 closed a few years ago.)
The station for Terminals 2 and 3 is between the two terminals and is reached by clearly signposted pedestrian tunnels. The stations for 4 and 5 are in the ...